Heat the oven to 190 C / 375 F. Arrange the baguette slices in a single layer on a rimmed baking sheet.

Brush both sides of each slice lightly with olive oil, reaching all the way to the edges. Sprinkle the tops with a pinch of flaky salt.

Bake for 10-12 minutes, flipping once halfway through, until the slices are pale gold and crisp. They will harden further as they cool. Transfer to a wire rack.

Check the trout fillets for any remaining pin bones by running your fingertip along the flesh. Remove any you find with tweezers or your fingers. Discard the skin.

Place the flaked trout into a medium mixing bowl. Add the crème fraîche, capers, lemon zest, lemon juice, horseradish, and chopped dill.

Fold everything together with a fork using a gentle, lifting motion until the mixture is just combined. You want visible flakes throughout, not a smooth paste.

Taste and season with flaky salt and black pepper. Press a piece of plastic wrap directly against the surface of the rillettes and refrigerate for at least 30 minutes before serving.

Remove the rillettes from the refrigerator and taste once more, adding a little extra lemon juice or salt if needed after chilling.

Spoon a generous amount of rillettes onto each crostino and garnish with a small dill sprig, a single caper, or a thin radish slice. Serve immediately.